Light emitting diodes (LEDs) are an efficient source of light. By utilizing a plurality of LEDs in a defined arrangement, the LEDs may be utilized to provide an alternative to current luminaires, such as incandescent bulbs and fluorescent tubes. In order for LED luminaires (e.g., bulbs, tubes, fixtures) to be widely adapted they need to be able to replace current luminaires (e.g., incandescent bulbs, fluorescent tubes) in existing lighting configurations (LED bulbs or tubes need to be retrofitted in the existing lighting configurations).
FIG. 1 illustrates a high level functional diagram of an example troffer 100 commonly used to provide fluorescent lighting in commercial establishments (e.g., office buildings, retail stores, apartment complexes, hotels). The troffer 100 includes a housing (not separately identified in the figure) that is typically located in the ceiling and houses a plurality of fluorescent tubes 110 (four illustrated). The troffer 100 includes clips 120 that are utilized to hold the fluorescent tubes 110 and to provide the appropriate power thereto. The tubes 110 need a high initial voltage to begin operation (lighting) and then require a constant current to operate. Accordingly, the troffer 100 includes a ballast 130 that receives the line power (e.g., 120V, 240V) for the establishment and provides an initial striking voltage to the tubes 110 to initiate operation and then maintains a constant current to the tubes 110. The troffer 110 includes wires incorporated therein (not illustrated) that connect the ballast 130 to the clips 120.
A retrofitted LED tube needs to have the same, substantially the same, or similar footprint and form factor (hereinafter, for ease, simply referred to as same footprint) to be able to replace the florescent tube 110 in the troffer 100. However, the power requirements for an LED tube are different than the power requirements for florescent tubes 110. The ballast 130 used with florescent tubes 110 is not capable of providing the power requirements of the LED tubes and is typically removed, disconnected, or deactivated (simply referred to hereinafter as removed for convenience) in retrofits. A power supply/driver is required to convert the line power to the appropriate power requirements of the LED tubes. Often retrofit LED tubes use individualized power supplies built into each tube and each tube is directly connected to the line power.
FIG. 2 illustrates a high level functional diagram of the example troffer 100 of FIG. 1 with example retrofitted LED tubes 210. The LED tubes 210 include individualized power supplies 220 therewithin. The line power is provided directly to the LED tubes 210 via the clips 120 as the ballast 130 was removed (the wires incorporated in the troffer that typically are used to connect the clips 120 to the ballast 130 are connected directly to the line power). The power supplies 220 convert the line power to the necessary power requirements of the LED tubes 210.
Requiring the ballast 130 to be removed and connecting the line power directly to the clips 120 adds to the labor costs of retrofitting the light troffers 100 with LED tubes 210. This operation may require skilled professionals (e.g., electricians) and may pose a safety hazard as contact with the line power may occur. Furthermore having the line power on the clips 120 may propose a hazard when the LED tubes 210 are replaced as an installer may inadvertently contact the line power.
Including the power supply 220 within the LED tube 210 limits the design parameters (e.g., size, configuration) associated therewith. Most built-in power supplies are low quality and typically fall far short in terms of safety and reliability. Furthermore, they are brittle and delicate making them prone to damage with regular shipping and handling. The cost of assembly and labor to include the power supply 220 within the LED tubes 210 is an additional hindrance. In addition, encapsulating the power supply 220 within the tube 210 generates additional unnecessary heat that is trapped therewithin. This additional heat adversely affects the LEDs themselves, altering color temperature and shortening their expected lifespan. Moreover, the power supply 220 may have a life span less then that of the LEDs and thus be the limiting factor in the life of the LED tubes 210.
Incandescent luminaires may be dimmed using a TRIAC dimmer that is typically used in place of an on/off switch. The TRIAC dimmer is designed to operate only when connected to a resistive incandescent load, which LED luminaires are not. The TRIAC dimmer in effect reduces the net energy applied to the incandescent luminaires and therefore reduces the light output. The operation of an LED is controlled by adjusting the current, as long as there is a sufficient voltage across the diode (between the anode and cathode). Even if TRIAC dimmers could function with LED luminaires, current power supplies and/or electronics associated with LED luminaires do not detect voltage changes caused by the TRIAC dimmer and therefore would not correctly modify the current based thereon in order to provide dimming.
What is needed is an external power supply for powering LED luminaires. The power supply should be rugged and dependable. The power supply may include useful and innovative features that make the LED retrofit safer as well as more robust and efficient. According to one embodiment, the power supply should isolate the dangerous line power from the LED luminaires (e.g., fixtures, bulbs, tubes, arrays). According to one embodiment, the power supply should have a footprint that makes retrofitting in an existing lighting system as simple as possible. According to one embodiment, the power supply should be capable of powering a plurality of LED luminaires (each LED luminaire possibly being powered individually). According to one embodiment, the power supply may be able to receive a line voltage as modified by a TRIAC dimmer or other dimming protocols and be able to drive the LED luminaires in such a fashion as to provide dimming.